1. Field of the Invention
The present invention relates to a liquid crystal display device comprising a backlight as a lighting system and particularly, to the liquid crystal display device whose motion picture performance is heightened by controlling the backlight.
2. Description of the Related Art
Although a CRT (Cathode Ray Tube) is a mainstream as a display device until now, these years an active matrix liquid crystal display device (hereinafter referred to as “LCD”) is pervading. The LCD is a display device utilizing light transparency of a liquid crystal, does not emit light by itself, and makes a display by transmitting/shielding light of a backlight located at a back face
Although there are many florescent tubes as the backlight of the LCD until now, in order to improve color reproductivity of a display image, these years there is a report of using a light emission diode (hereinafter referred to as “LED” as the backlight, for example, a non-patent document 1 of SID Digest pp. 1154 in 2002 and the like. Because in this LED backlight a temperature property of a red (hereinafter referred to as “R”) LED is different from those of a green (hereinafter referred to as “G”) LED and a blue (hereinafter referred to as “B”) LED, it is necessary to provide an adequate feedback circuit in order to display a same color over long hours.
On the other hand, for example, it is reported a system of performing a color adjustment by displacing emission periods of the three colors RGB, configuring feedback circuits of the three colors by one sensor, and adjusting the emission period of each color as in presentations of a non patent document 2 of p. 25 of IEICE 2002-35 (2002-09) in Technical Report of the Institute of Electronics, Information and Communication Engineers and a non patent document 3 of Color Forum Japan 2002, 6-3.
In addition, as a luminance adjustment method of the LED backlight is shown a method (Pulse Width Modulation, hereinafter referred to as “PWM”) of adjusting luminance by adjusting an emission period for each LED as in FIG. 16 of a patent document 1 of Japanese Patent Laid-Open Publication No. 2001-272938.
But if controlling the emission periods of the LCD of the three colors RGB by methods in the patent document 1 and the non patent document 2, there occurs a phenomenon of coloring inside an edge blur in displaying a motion picture because emission timing and emission centers of the three colors RGB are displaced.
A phenomenon of the edge blur in displaying the motion picture in an LCD is reported at pp. 19-26 (1996-06) of IEICE 96-4 in Technical Report of the Institute of Electronics, Information and Communication Engineers and the like. According to these, the blur occurs at an edge of a motion image due to a discord between the motion image of a hold-type display and an eye movement by a pursuit of a human being.
Here will be described coloring at an edge when making an LED of each color of the RGB the PWM control as in the patent document 1 with using the LED as the backlight, referring to FIG. 16.
In an upper portion of FIG. 16 a vertical axis is time and a horizontal one is a moving direction of a motion picture display object on an LCD. The each LED of the RGB simultaneously lights, and emission intensity thereof is different according to the color; therefore, for example, the PWM control of extinguishing the LED in order of the B, R, and G is performed.
On the other hand, a lower portion of FIG. 16 shows a brightness property when a human being's eyes see the image of the motion picture display object. A horizontal axis is a moving direction and a vertical one is brightness. Because when the human being's eyes see a moving object, they observe it while following in the moving direction and recognize an integration value as brightness, at an edge of a side of the object moving direction firstly B is strong, R joins therein, and lastly G joins therein, and thus white results in being displayed. On the other hand, at the edge of the opposite side of the object moving direction firstly B disappears, next R decreases, and lastly G results in remaining.
In addition, according to the same principle, the coloring similarly occurs at an edge of a motion picture display when the emission periods of the RGB are displaced as in the non patent documents 2 and 3.
Consequently, also when emission elements of individual control of the three-color RGB such as an LED are used as a backlight, a liquid crystal display device is strongly requested that can clearly display a motion picture without generating the coloring at an edge blur portion in displaying the motion picture.